DE10259051A1 - Channel allocation in cellular radio communications system involves determining channel for mobile, base station connection for which common and adjacent channel interferences do not exceed threshold - Google Patents

Abstract

The method involves determining a channel for a connection in a cell between a mobile station and a base station as the channel for which common channel interferences and adjacent channel interferences from the same cell do not exceed a defined threshold, whereby channels used in the same cell and in adjacent cells by active mobile stations are taken into consideration.

Description

Serve radio communication systems the transfer of information, voice or data, with the help of electromagnetic Waves over a radio interface, also called air interface, between a transmitting and a receiving radio station. The radio interface is in channels organized that are distinguishable and the individual participants be assigned to.

In the well-known GSM mobile radio system, as well as its further development with a packet data service GPRS respectively EGPRS, whose architecture is described, for example, in B. Walke "Mobile Networks and their logs ", Volume 1, Teubner-Verlag Stuttgart, 1998, pages 138 to 151, and Pages 295 to 311 describes a channel through a narrow band Frequency range and a time slot formed. Since there is a subscriber signal can differ in frequency and time in one channel from the other subscriber signals the radio station detects the data of the subscriber signal. In newer radio communication systems, such as the UMTS system, the individual participants about it distinguished by different spreading codes.

Because there is only one in a cellular network limited number of different channels is available, the area which is to be served by the mobile radio network, divided into cells. A subset of different channels is assigned to each cell. Same channels can in spatially removed cells can be reused. The distance at the same channels on the one hand determines the capacity of the mobile radio system, and on the other hand, interference immunity. In the GSM system, in which channels differentiated by different frequencies, From this was called "frequency repetition distance" or trap. With a view to a possible size capacity of the cellular network, it is advantageous to have a small distance choose, with regard to interference immunity it is advantageous to keep the distance as large as possible to choose. In terms of These conflicting requirements must therefore be compromised become.

There are GSM networks in a 1: 1 Reuse operated, i.e. every frequency is used in every cell. However, a frequency hopping method with different ones is used Frequency hopping systems per radio link, so depending on the load condition more or less burst collisions occur. In this case a channel through a time slot and a frequency hopping system Are defined.

Disorders occur on the one hand by cellular subscribers who are in the same cell Use channel, so-called co-channel interference, on the other hand through Cellular subscribers operating in the same or in neighboring cells use an adjacent channel, so-called adjacent channel interference.

In the literature you can find the In terms of channel assignment, the DFCA solution (Dynamic Frequency and Channel Allocation), see Halonen et al, “GSM, GPRS and EDGE Performance, "Wiley 2002, pp. 299ff.

The invention is based on the problem to specify a method for channel allocation in a mobile radio system, with the one hand the achievable capacity of the radio communication system and on the other hand, interference immunity be enlarged can. In particular, are supposed to DFCA can be achieved through significant performance gains.

According to the invention, this problem is solved by a method according to claim 1. Further embodiments of the invention emerge from the remaining claims.

In the method according to the invention becomes the channel assignment for a connection in a cell between a mobile station and one Base station determines the channel for which co-channel interference and adjacent channel interference are used neighboring cells and adjacent channel interference from the same cell do not exceed a predetermined threshold, being those in the same cell and in neighboring cells by active Mobile stations use channels considered become. In the method according to the invention is thus from a rigid assignment of certain channels to certain Cells deviated. Rather, it looks at which channels are occupied and how this channel assignment in the considered Cell and in the neighboring cells on the new connection to be established in terms of of disturbances impact. For the new connection to be established is then selected for that channel tolerable disorder is to be expected. That can e.g. B. the channel with the lowest disorder be or a channel for does not exceed a threshold dependent on the respective service becomes. By considering depending on the service Threshold ensures that the services request of the person concerned Participant met becomes.

When considering the expected interference, only the adjacent channel interference from the considered cell and the neighboring cells and co-channel interference from neighboring cells. Co-channel interference and adjacent-channel interference from more distant cells can be weighted using an interference matrix. In this way, the channel to be established is assigned the channel for which a still tolerable fault can be expected. On the other hand, the available channels are used in the best possible way with optimal interference immunity. Since the capacity of the radio communication system is increased.

In the calculation of the channel assignment can additionally the interference elimination options for Example by interference cancellation of network and mobile station incorporated.

Sector-shaped cells can be used as neighboring cells considered, which are covered by the same sector antenna. It can also be cells that are covered by different antennas. If the cells are assigned to different base station controls, It must be ensured that information is available in the individual cells active channels available in a central instance are.

Preferably, when assigning channels the positions of active mobile stations within the neighboring Cells i.e. takes into account the location information of the active mobile stations. In this way, the capacity of the radio communication system can be further increased because of the positions of the occupied channels taken into account within the cells become.

Furthermore, the available ones can also be used Radio parameters and measured values are used. This includes power Control information, distance or timing advance etc. It can be taken into account, for example whether a mobile station active in a neighboring cell with less or high power sends.

It is within the scope of the invention to subdivide the cells into partial areas by means of beam shaping. In this case, the beam shaping preferably becomes the position of active mobile stations within the neighboring or the same Cell derived. For the determination of the position of the active mobile stations is according to this embodiment no additional Position determination required. Alternatively, in the case of cells the position from the radio parameters without beam shaping sections determines and / or localization information (for example LCS) be used.

In view of that co-channel interference from neighboring cells, the adjacent channel interference from neighboring cells and the adjacent channel interference different influence on the overall disorder of one from the same cell Have connection, it is advantageous to use these with different Weights to take into account. In particular, networks and subscriber stations with the possibility of interference elimination can be one certain number of sources of interference steam individually, what takes into account can be.

The method is particularly applicable in a radio communication system in which each channel is through one Time slot and a frequency is defined. So it is special applicable in a radio communication system according to the GSM standard, GPRS, EDGE and the TDMA standard. The procedure is also suitable for all FDMA systems as well as for Systems based on CDMA (e.g. UMTS, TD-SCDMA), here one Channel is defined by a code or a code time slot pair.

Is a channel through a time slot and a frequency is determined, so when determining the one to be assigned Channel for a predetermined time slot for each unused frequency value takes into account whether the same frequency value is used in the neighboring cells, and whether adjacent frequency values in the neighboring cells or the same cell. For the Channel assignment uses the frequency value for which it is the same Frequency value in if possible few neighboring cells and / or adjacent frequency values in preferably few neighboring cells or the same cell can be used. at additional Applying interference elimination can do some well-defined number of collisions.

It is within the scope of the invention of a neighboring cell in which the same frequency value is used, one first value, an adjacent cell in which an adjacent frequency value is used, a second value and the same cell in which a adjacent frequency value is used to assign a third value. To assess the fault is subsequently the sum of the assigned first values, second Values and third values. It becomes the channel with the one Frequency assigned for that the sum does not exceed the specified threshold. Doing so is neighboring Cells in which neither the same frequency value is used nor an adjacent frequency value is used, no value assigned. As well no value is assigned to the same cell if there is no value in it Channel with an adjacent frequency is active. In this way is the height the sum is a measure of how many potential (and possibly not eliminable) interferers are in the same cell or neighboring cells.

These values can be values or costs a target function based on the existing radio parameters, the positions of cells and participants, the interference matrices as well as the interference elimination capabilities determined and modified by network and mobile station.

It is within the scope of the invention to specify a threshold with which the sum is compared. If the sum is above the specified threshold, no channel is assigned. In this way, load control of the radio communication system is effected. By inserting the threshold, a be agreed interference immunity guaranteed. Of course, this comes at the expense of the capacity of the radio communication system. If the threshold is exceeded, known load defense mechanisms can also intervene, for example handover in neighboring cells that are less loaded.

The procedure is used for dual-band cells for each single band performed. Depending on the availability of the Different thresholds are set for resources. With dual band Load balancing is also preferably used for cells, i.e. the participant is assigned to the band with the lower relative load.

The invention is described below of an embodiment, that is shown in the figures, explained in more detail.

1 shows a section of the architecture of a radio communication system.

2 shows a channel assignment scheme for three cells and twelve channels.

3 shows a channel assignment scheme for three cells and twelve channels taking into account the positions within the cells.

A radio communication system comprises a plurality of base stations BTS (see 1 ). Each base station BTS is connected to a base station controller BSC. A base station controller BSC can have several base stations BTS assigned to it. The base station controls BSC represent a connection to a mobile switching station MSC. The mobile switching station MSC represents a connection to other mobile switching stations and other switching centers, for example to packet data services or to the fixed network.

The base stations BTS are radio stations over which a radio connection to a mobile station MS can be established. Common today Base stations BTS are equipped with a sector antenna via which them into three independent sectorial Radiate cells S1, S2, S3. Place the sector-shaped cells S1, S2, S3 neighboring cells.

To establish a connection between the mobile station MS and the base station BTS becomes the connection assigned a channel. In the GSM system the channel is indicated of a time slot and a frequency. In the GSM system the time slot by specifying a TDMA (Time Division Multiple Access) frame number and the number of the time slot in the relevant frame and the frequency by specifying the for connections to mobile stations to disposal standing frequencies MA, as well as an offset MAIO in frequency or the frequency hopping system.

To assign a channel for a connection to be set up, a channel assignment scheme for three adjacent sectors is considered in a first exemplary embodiment of the method according to the invention (see 2 ). The considered sectors and the available channels are shown in table form in the channel assignment scheme. The rows of the table are assigned to the sectors under consideration, a first sector S1, a second sector S2 and a third sector S3. The columns of the table are the channels that are designated by the channel parameters F ₀ , F ₁ , F ₂ , F ₃ , F ₄ , F ₅ , F ₆ , F ₇ , F ₈ , F ₉ , F ₁₀ , and F ₁₁ , The channel parameters are, for example, frequencies or offset numbers to a frequency value. In the channel assignment scheme, active channels K _{a are identified} by hatching in the respective sector S _i . Inactive channels in the sectors S _i are identified by white fields K _n . Channels K _U to be examined are identified by crossed hatching. For the channels K _U to be examined, an assessment is made as to which of the channels K _U to be examined is experiencing the least interference.

To assess interference due to interference, the possible interference is classified as follows: A co-channel interference from a neighboring sector is present if the same channel with the same frequency is active in the neighboring sector. An adjacent channel interference from a neighboring sector is present if an adjacent channel is active in the neighboring sector, that is to say a channel with a channel parameter f _{j − 1} or f _{j + l} if the channel parameter f _{j is} occupied in the channel to be examined. An adjacent channel interference from your own sector exists if an adjacent channel is active in your own sector. The different possible disturbances have different serious effects. These differences are taken into account by assigning different weight factors. For example, the adjacent channel interference from the neighboring sector is assigned the value 1, the adjacent channel interference from its own sector is assigned the value 3 and the co-channel interference from the adjacent sector is assigned the value 5.

If one considers the expected interference for the channel K _U to be examined in the second sector S2 with the channel parameter F ₄ , the result is 1 + 1 + 3 + 5 = 10.

For the channel K _U to be examined in the second sector S2 with the channel parameter F ₇ , 1 + 1 + 3 + 3 + 5 + 5 = 18 results.

That means for the channel K _U to be examined in the second sector 52 With the channel parameter F ₇ , a greater disturbance is expected than for the channel K _U to be examined in the second sector S2 with the channel parameter F ₄ . The channel K _U to be examined is thus assigned to the connection in the second sector S2 with the channel parameter F ₄ .

The weight factors determine the behavior of the algorithm. The values of the weight factors must therefore be chosen so that they increase in accordance with the severity of the interference. The values of the weight factors are obtained, for example, from measurements of the radio parameters, the mutual gene cell disorders, for example in the form of an interference matrix, the interference elimination possibilities of the network and subscriber stations and the positions of cells and subscriber stations, if available, derived and determined.

In a second embodiment the method is used for channel assignment in a radio communication system, in which the sectors are divided into sub-sectors. Doing so using stronger narrow beam Antennas broadcast the radio field on the sub-area of the sector concentrated in which the participant is staying. A new connection to be established will first operated with a radio beam that covers the entire sector. Below, if it is determined based on field strength measurements, where the participant is within the sector, the Bundled radio beam.

To determine a channel to be assigned, a channel assignment scheme is again considered (see 3 ). The channels active in a sector or a sub-sector are plotted in a table. A first sector S1, a second sector S2 and a third sector S3 are assigned to the rows. Channel parameters F ₀ , F ₁ , F ₂ , F ₃ , F ₄ , F ₅ , F ₆ , F ₇ , Fe, F ₉ , F ₁₀ and F _{11 are} assigned to the columns. For example, the frequency offset numbers common in the GSM system can be used as channel parameters.

Active channels K _a are shown hatched in the channel assignment diagram. The entire sector area is hatched for connections for which no switchover to a subsector has yet taken place. For connections where a switchover to a subsector has taken place, only the subsector is hatched. Inactive channels K _n are marked by white fields.

In the following, the second sector S2 with the channel parameter F ₄ and the second sector S2 with the channel parameter F _{7 are} considered as the channels K _U to be examined. The channels K _U to be examined are identified by crossed hatching.

The weight factors are as in first embodiment assigned. Add to that for subsectors Additional factors introduced become. It will be for the neighboring sub-sector the additional factor 1, for the next sub-sector the additional factor 0.7, for for the third sub-sector the additional factor of 0.4 and for the fourth, furthest distant sub-sector defined the additional factor 0.1. These are exemplary Additional factors are used to assess the disorder Neighboring sectors. When assessing the disruption from your own sector however, each sub-sector is considered to be an equally strong disruption.

This results for the channel Ku to be examined in the second sector S2 with the channel parameter F ₄ 1 × 0.7 + 1 × 0.4 + 3 + 5 × 0.1 = 4.6.

For the channel K _U to be examined in the second sector S2 with the channel parameter F ₇ results 1 × 1 + 1 × 0.4 + 3 + 3 + 5 × 0.7 + 5 × 0.4 = 12.9.

This approach takes into account where a participant with an active channel K _{a is located} in a neighboring sector. The effect of the disorder differs depending on the location.

In addition, the possibility disturbers through interference elimination to take into account or those based on radio parameters, for example the transmission power or the distance channel assignment derived from a timing advance value considered become. Interference elimination options as well as the calculation of radio parameters and interference matrices was in the above calculation examples the overview because not yet considered.

The consideration is for the whole second sector S2 performed. When switching to the subsector corresponding to the subscriber the assignment remains in the second sector S2. By switching the disturbance is reduced to the concrete sub-sector Interference.

The above embodiment can be now starting from one base station location to the neighboring one Expand locations or cells or even network-wide.

• – GSM-Netz mit 72 Drei-Sektorstandorten (216 Zellen)
• – Subsektorierung mit vier Subsektoren in allen Fällen
• – 12 Frequenzen für reine Verkehrskanäle
• – An jedem Standort wird derselbe Satz von Frequenzen benutzt, das heisst, Frequenzwiederholfaktor 1 × 1
• – Anzahl der Frequenzen für Verkehrskanäle (TCH-Frequenzen) pro Zelle: 6 beziehungsweise 7

The method according to the invention was tested with the aid of a simulation program. A number of quality parameters are calculated in the simulation program for a GSM network, whereby realistic propagation conditions are assumed. For example, the blocking probability, the probability of poor quality of a call, the probability of bit errors and the like are calculated. The capacity of the radio communication network and a location is subsequently determined from this data. The capacity is determined as the market value in Erlang, which can be managed from one location without the quality falling below a predetermined threshold. The value is related to the total number of available time slots. This makes it independent of the number of carrier frequencies. The value obtained in this way is often referred to in the literature as "Erlang Fractional Load". The following network parameters were specified in the simulation:

• - GSM network with 72 three-sector locations (216 cells)
• - Subsectoration with four subsectors in all cases
• - 12 frequencies for pure traffic channels
• - The same set of frequencies is used at each location, i.e. frequency repetition factor 1 × 1
• - Number of frequencies for traffic channels (TCH frequencies) per cell: 6 or 7

Simulation parameters:

• - Number of conversations 100,000 in the simulation
• - weight factors 1 for adjacent channel interference the neighboring sector, 3 for Adjacent channel interference from our own sector, 5 for Co-channel interference from the neighboring sector
• - additional factors for subsectors: 1; 0.7; 0.4; 0.1
• - interference threshold for weighted Total: 9, which means that a channel to be examined is only assigned if a total value <9 otherwise the conversation is rejected.

Simulation results:

Capacity 1 is the value that is without weighting the sub-sectors, that is, without including the Location information, as explained with reference to the first embodiment.

Capacity 2 is the result of that including the location information in the channel algorithm, as it is based on the second embodiment explained was yielded.

It turns out that the consideration the location information, as explained using the second exemplary embodiment, a Increase in capacity from 23 to 25%.

A consideration of the interference elimination options network and subscriber stations as well as the consideration the channel assignments in different cells and their mutual interaction as well as consideration further radio parameters leave even more collisions between channels in different cells too. This allows the channel trap in the network again significantly increased, so that the total network capacity drastically is increased.

Claims (12)

Procedure for channel assignment in a cellular Radio communication system in which channel assignment for a connection in a cell between a mobile station and a base station which channel is intended for the co-channel interference and adjacent channel interference from neighboring cells and adjacent channel interference from the same cell do not exceed a predetermined threshold, being those in the same cell and in neighboring cells channels used by active mobile stations are taken into account. A method according to claim 1, wherein in the channel assignment the positions of active mobile stations within neighboring ones Cells become. Method according to one of claim 2, - in which the cells are divided into sub-areas by means of beam shaping of antennas become, - at the positions of the active mobile stations from the beam shaping can be derived within the respective cells. Method according to claim 2, - in the case of radio parameters or the position with the help of localization services of the active mobile stations is determined. A method according to any one of claims 1 to 4, in which interference elimination capabilities from the mobile station and / or base station are taken into account. Method according to one of claims 1 to 5, in which faults and / or Interactions between different cells as an interference matrix weighted in the calculation. Method according to one of claims 1 to 6, in which for determining a channel system is considered in which the Positions of active mobile stations and cells, interference elimination, the radio parameters of the active mobile stations and the base stations, the co-channel interference from neighboring cells, the adjacent channel interference from neighboring cells and the adjacent channel interference same cell with different weights become. Method according to one of claims 1 to 7, wherein the channel through a time slot and a frequency or a frequency hopping system or is defined by a code in CDMA systems. A method according to claim 8, wherein in the determination of the channel for a predetermined time slot for every unused frequency value is taken into account whether it is the same Frequency value is used in the neighboring cells and whether neighboring ones Frequency values in the neighboring cells or in the same cell be used. Method according to claim 9, - that of a neighboring cell, in which the same frequency value is used, a first value, one neighboring cell in which an adjacent frequency value is used becomes a second value, the same cell in which an adjacent Frequency value is used, a third value is assigned, - in which to assess the disorder the sum of the assigned first values, second values and third Values is formed - at to which the channel with the frequency for which the Sum does not exceed a predetermined threshold. A method according to claim 10, - in which the radio parameters and position of the subscriber stations / cells as well the interference elimination capabilities be included in the first, second and third values. The method of claim 10 or 11, wherein the determined channel is only assigned if the sum is one of the Service requirements of the subscriber station do not exceed the threshold dependent.